There are many situations in which a throttling device having a variable area of opening is useful to introduce a variable pressure drop in a chemical or industrial system in which fluid is transported from one place to the other. Under most circumstances, it is important that an absolute minimum resistance to flow is provided in a fully open position, to maximize flow, maximize energy conservation, and/or to minimize upstream pressure. Also in many circumstances it is important that the throttling device not be completely closable since that may disturb system flows, so that serious process upsets occur, or even dangerous conditions.
In order to obtain effective throttling with an absolute minimum pressure drop in the open position, oftentimes a line size full bore ball valve is used, with a minimum height and opening stop added where necessary. However, in many situations the cost of that type of valve is prohibitive, in which case a butterfly valve is often substituted. However, a butterfly valve compromises the objective of lowest possible resistance in the open position. Sometimes gate valves are utilized; however, they have the problems of deposits from flowing fluid get caught in the gate recess in the body, preventing proper stroking of the valve, and also the throttling characteristics and efficiency are not as good as for ball valves or butterfly valves.
According to the present invention a throttling element for a throttling device, and throttling device per se, are provided which combine all of the advantages of the butterfly and full bore ball valves with none of the disadvantages. According to the present invention a throttling device is provided that has a full bore when wide open, throttling capability which is easily and positively adjusted, and is designed so that it cannot completely close (or substantially completely close) off the line, yet it has a cost that is significantly less than conventional full bore balls and typically in the same range of cost as butterfly valves.
The throttling device according to the present invention may be utilized in a wide variety of different environments. For example, one environment is in the field of heating and ventilating where air delivery systems must be balanced in various parts by adjusting valve openings, and when low resistance is needed, an absolute lowest possible resistance improving energy efficiency dramatically. Also, the throttling device according to the invention finds significant use in the field of manufacture of petroleum coke. In that field it is often required to warm up the next drum to be filled using the hot (850-900.degree. F.) vapors coming from the drum that is still being filled. To force some of the vapors to flow through the drum that is to be warmed up a back pressure valve is typically provided in the return line to the fractionator, the back pressure valve being a throttling valve which creates a pressure rise upstream of the valve thereby forcing some of the vapors to flow into the drum to be warmed up. When used in the throttle mode to create a pressure drop, it is important that this valve not be allowed to close fully since to do so would upset the process. By utilizing the valve according to the present invention even in this unusual and demanding environment containing high temperature, and contaminants in the fluid being throttled, which may result in solids build up on surfaces, the throttling device according to the invention is very effective. The invention is also effective in a wide variety of other environments.
According to one aspect of the present invention a throttling element per se is provided comprising: An annular metal substantially spherical segment having an exterior arcuate extent of about 80.degree. or less. And first and second elongated metal shaft stubs extending radially outwardly from the exterior of the annular substantially spherical segment, on opposite sides of the segment in the dimension of elongation of the shaft stubs. For example, the exterior arcuate surface extent may be about 60-70.degree.. A scalloped circumferential passage may be provided surrounding the arcuate exterior of the segment and extending substantially perpendicular to the shaft stubs.
While the shaft stubs may be integral with the segment, they also may be separable. One exemplary way that they may be separable is to provide each of the shaft stubs with at least one key-receiving slot parallel to the dimension of elongation and at least one key extending between the segmented shaft disposed in the slot for holding a shaft stub to the segment. A bore may be formed in the segment exterior adjacent each of the shaft stubs through which a key extends into association with a slot.
The throttling element typically provided in combination with the housing having an interior bore with a first diameter and a substantially spherical second interior surface cooperating with the throttling element exterior, the housing receiving the shaft stub so that the throttling element is rotatable about an axis defined by the stubs. The annular throttling element has an interior bore with a second diameter, the second diameter substantially the same as the first diameter so that the throttling element provides minimum resistance of fluid flow through the housing interior bore when in a fully open position, and wherein the second diameter and the arcuate extent of the segment are so dimensioned that the throttling element cannot preclude or substantially preclude flow through the housing interior bore regardless of what position it is rotated to about the axis.
The housing may have a width between first and second sides thereof that is only slightly greater than the annular segment width, and first and second housing extensions may extend from the first and second sides of the housing. A spacing is typically provided between the substantially spherical segment interior of the housing and the exterior of the annular segment, the spacing typically being between about 0.25-0.5 inches, and substantially uniform (although slightly greater where the scalloped circumferential passage is provided, when utilized). The housing may be two piece having a parting line substantially parallel to the axis, and releasable fasteners (e.g. bolts) may be provided for holding the housing pieces together at the parting line during operation and releasable to allow removal of the annular segment. Typically the annular element has a width that is between about 50%-70% of the first diameter.
According to another aspect of the present invention a throttling device is provided comprising the following components: A housing having an interior bore with a first diameter through which fluid to be throttled flows. An annular throttling element. Means for mounting the throttling element to the housing for rotation about an axis substantially perpendicular to the housing bore. The throttling element having an interior bore with a second diameter, the second diameter substantially the same as the first diameter so that the throttling element provides minimum resistance of fluid flow through the housing interior bore when in a fully open position. And the throttling element having an exterior extent with a first width, and wherein the second diameter and the first width are so dimensioned that the throttling element cannot preclude or substantially preclude fluid flow through the housing interior bore regardless of what position the throttling element is rotated to about the axis.
The details of the throttling element, and the housing, preferably are as described above. At least one steam purge connection may also be provided to the circumferential passage on each side of the shaft stubs. The rotating means may comprise first and second shaft stubs, or may comprise only a single shaft stub, or multiple shaft stubs, or other surface manifestations beside shaft stubs, or simply bearing surfaces themselves depending upon the particular use to which the device is put. Whatever the rotating means, it typically is readily connected up to conventional and standard rotary actuators, which may be either hand, electric, pneumatic, hydraulic, or otherwise operated.
It is a primary object of the present invention to provide the throttling of fluid flow using a device which has the absolute minimum possible pressure drop in the open position, effectively and accurately throttles in a wide variety of ranges (e.g. providing throttling of any amount between 0% to about 70%), yet has the same cost range as a butterfly valve, and will not be severely adversely affected by contaminants in the fluid being throttled, and is easy to service or replace. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.